In vehicles such as automobiles, engine power drives an alternator (a generator) to generate electric power that is used to charge a secondary battery. The electric power stored in the secondary battery is then used to drive various loads (such as an electric power steering system).
In recent years, technologies for using the alternator to convert the kinetic energy of the vehicle to electrical energy as the vehicle is decelerating and storing the resulting electric power in the secondary battery have been proposed.
For example, Patent Document 1 discloses a technology in which the voltage of the alternator is set to high as the vehicle is decelerating in order to regeneratively store electric power in the secondary battery. Moreover, Patent Document 2 discloses a technology in which the charge current is used to estimate the amount of charge (SOC) of the secondary battery and the secondary battery is regeneratively charged on the basis of that estimation. Patent Documents 3 and 4 disclose technologies in which two electric power storage devices are used to perform regenerative charging efficiently.